<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>重复请求问题</title>
</head>

<body>
    <button>点击发送</button>
    <script>
        //获取元素对象
        const btns = document.querySelectorAll('button');
        let x = null;
        //标识变量
        let isSending = false; //是否正在发送AJAX请求

        btns[0].onclick = function() {
            //判断标识变量
            if (isSending) {
                x.abort(); //如果正在发送，则取消该请求，创建一个新的请求
            }
            x = new XMLHttpRequest();
            //修改标识变量
            isSending = true;
            x.open("GET", 'http://127.0.0.1:8000/delay');
            x.send();
            x.onreadystatechange = function() {
                if (x.readyState === 4) {
                    //修改标识变量
                    isSending = false;
                }
            }
        }
    </script>
</body>

</html>